1. Field of the Invention
The present invention relates to wiring repair apparatuses for repairing defective parts of wiring formed on a substrate and, particularly, it relates to a wiring repair apparatus for repairing breaks in wiring by laser chemical vapor deposition (CVD).
2. Description of the Related Art
Liquid crystal displays (LCDS) have become rapidly widespread over the past several years. This trend is being driven by LCDs based on semiconductor thin-film transistor (TFT) technology. There are two types of TFTs: amorphous silicon (a-Si) TFTs and polysilicon (poly-Si) TFTs. These two types of TFTs have similar principles and structures. As LCDs have recently become larger, defects such as shorts and breaks occur more frequently in the wiring of integrated circuits, including TFTs and their peripheries.
FIG. 1 is an equivalent circuit diagram of an LCD. FIG. 2 is a partial sectional view of a TFT in the LCD. In FIG. 1, an LCD 101 includes a first glass substrate 102 (see FIG. 2), a second glass substrate (not shown in the drawings) opposed to the first glass substrate 102, and a liquid crystal layer (not shown in the drawings) disposed between the first glass substrate 102 and the second glass substrate. A common electrode C is formed on the surface of the second glass substrate facing the first glass substrate 102. Gate lines G1 to Gm (m is a natural number) and source lines S1 to Sn (n is a natural number) are provided on the surface of the first glass substrate 102 facing the second glass substrate. The gate lines G extend in parallel in a row direction while the source lines S extend in parallel in a column direction.
In plan view, (m×n) pixels 104 are arranged in a matrix. These pixels 104 correspond to the areas where the gate lines G and the source lines S intersect each other. Each pixel 104 includes a metal-oxide semiconductor field-effect transistor (MOSFET) 105 and a capacitor 106. The MOSFET 105 is a TFT. The source of the MOSFET 105 is connected to any source line S. The gate of the MOSFET 105 is connected to any gate line G. The drain of the MOSFET 105 is connected to one electrode of the capacitor 106. The drain of the MOSFET 105 and the common electrode C apply voltage to a liquid crystal cell 103. The other electrode of the capacitor 106 is connected to a capacitor electrode Cs. The liquid crystal cell 103 is the part of the liquid crystal layer corresponding to each pixel 104. In other words, the collection of the liquid crystal cells 103 constitutes the liquid crystal layer.
Referring to FIG. 2, a gate electrode 107 connected to any gate line G (see FIG. 1) is provided on the first glass substrate 102. A gate-insulating film 108 covering the gate electrode 107 is provided on the overall surface of the first glass substrate 102. A functional film 109 composed of amorphous silicon (a-Si) is formed on the gate-insulating film 108 above the gate electrode 107. This functional film 109 constitutes the channel region of the MOSFET 105 and includes a lower layer 109a composed of a-Si and an upper layer 109b composed of n-doped amorphous silicon (n+ a-Si). One end of the functional film 109 is covered with a source electrode 110 connected to any source line S (see FIG. 1) while another end of the functional film 109 is covered with a drain electrode 111 connected to the capacitor 106 (see FIG. 1). A protective film 112 covers the functional film 109, the source electrode 110, and the drain electrode 111.
In the manufacturing process of the LCD in FIGS. 1 and 2, defects such as breaks may occur in the source lines S, the gate lines G, the gate electrodes 107, the source electrodes 110, the drain electrodes 111, and the like (hereinafter collectively referred to as wiring) because of defective conditions in deposition, exposure, etching, and cleaning or the intrusion of airborne foreign particles in the clean room. Such defects cannot be completely avoided with any current advanced technology.
Laser repair technique has been expected to improve the yield of LCDs. In particular, techniques for breaking a short or shorting wiring between the upper and lower layers have become widespread in TFT manufacturing processes. For example, Japanese Patent Publication Laid Open No. 2000-328247 and No. hei 10-324973, to the present assignee, have disclosed a novel method for repairing breaks by laser CVD. This laser CVD technique has been put on the market to gain international recognition.
According to this laser CVD technique, tungsten (W) or chromium (Cr) is deposited on a break in wiring to repair the break. This laser CVD technique enables non-contact, non-heating repair of a defective part in a short time with the part kept in a dry state. Currently, every TFT-LCD manufacturer depends on this laser CVD technique as a wiring repair technique.
The above conventional technique, however, has the following problem. When a break in wiring is repaired by laser CVD, the material for deposition on the break is most preferably the same as that constituting the wiring. For example, an aluminum (Al) film is preferably deposited on a break in Al wiring by laser CVD, and a chromium (Cr) film is preferably deposited on a break in Cr wiring by laser CVD. Such repair provides wiring with uniform electrical conductivity. And, it provides wiring with uniform thermal expansivity, and therefore it makes heat load resistance of the wiring improve.
Most TFT-LCDs have wiring including two or more different materials. Table 1 shows materials for individual components of TFT-LCDs. This table 1 is sourced from “Liquid crystal device handbook,” issued by Nikkan Kogyo Shimbun, Ltd. According to Table 1, typical materials for wiring and electrodes in TFT-LCDs include metals such as Al, molybdenum (Mo), and Cr. Currently, most TFT-LCDs have wiring including different materials; an example is wiring including Al gate lines and Cr source lines.
TABLE 1ComponentMaterialTFTFunctional filma-Si, n+ a-Si, poly-SiInsulating filmSi3N4Protective filmSiNxElectrode filmAl, Mo, CrMIMMetal filmTa, CrInsulating FilmTaxOyPixel electrodeITO(In2O3 + Sn), IO(In2O3)Alignment filmpolyimide, SiOx
As described above, however, normal laser CVD apparatuses can deposit only one material (for example, either W or Cr). If, for example, TFT-LCD wiring including Al gate lines and Cr source lines is repaired with a laser CVD apparatus capable of Cr deposition, the Cr source lines can be successfully repaired but the Al gate lines undesirably include parts repaired with Cr. Such repaired parts, having non-uniform electrical conductivity and non-uniform thermal expansivity, cause thermal stress when a heat load is applied. The repaired wiring therefore has the disadvantage of reliability.
An approach to the problem described above is the use of the same number of laser CVD apparatuses as the materials used for wiring. In the above example, according to this approach, the gate lines are repaired with a first laser CVD apparatus capable of Al deposition while the source lines are repaired with a second laser CVD apparatus capable of Cr deposition. This approach, however, requires a plurality of laser CVD apparatuses, thus having the problems that the equipment cost increases and the repair efficiency decreases.
Another approach is the replacement of a feedstock for CVD with another feedstock in a single laser CVD apparatus. In the above example, according to this approach, dimethylaluminum hydride (DMAH) is supplied to a laser CVD apparatus as a feedstock for Al deposition to repair the gate lines, and chromium hexacarbonyl (Cr(CO)6) is then supplied to the laser CVD apparatus as a feedstock for Cr deposition to repair the source lines.
This approach, however, encounters the problem that a single laser CVD apparatus has difficulty in processing different feedstocks because they require different processes for generating a source gas for CVD. In the above example, DMAH, which is a feedstock for Al, is normally a liquid and is therefore vaporized to generate a source gas for CVD. On the other hand, Cr(CO)6, which is a feedstock for Cr, is normally a solid and is therefore sublimated to generate a source gas for CVD. Thus, a single laser CVD apparatus has difficulty in processing both DMAH and Cr(CO)6 because they require different processes for generating a source gas.